1. Field of the Invention
The present invention relates to a stereoscopic display device capable of electrically switching over between two-dimensional displaying and three-dimensional displaying by using a variable lens-array element utilizing a liquid crystal lens.
2. Description of Related Art
There has been known a binocular stereoscopic display device or a multi-eye stereoscopic display device, which realizes a stereoscopic vision by presenting parallax images, having parallax, to both eyes of an observer, respectively. There is also a spatial-image stereoscopic display device, which realizes more natural stereoscopic vision. The spatial-image stereoscopic display device radiates a plurality of light rays having different radiation directions into a space, to form a spatial image corresponding to a plurality of viewing angles.
As a way of realizing such stereoscopic display devices, there has been known a stereoscopic display device, which combines a two-dimensional display device such as a liquid crystal display with an optical device used for a three-dimensional displaying, for example. This optical device for the three-dimensional displaying application deflects display-image light emitted from the two-dimensional display device into a plurality of viewing-angle directions. As illustrated in FIG. 19, a cylindrical lens array 302, in which a plurality of cylindrical lenses (cylinder lenses) 303 are arranged in parallel, is utilized for example for the optical device. The cylindrical lens array 302 is disposed to oppose a display screen of a display panel 301 which includes the two-dimensional display device. Each of the cylindrical lenses 303 is so disposed as to extend vertically (or a “vertical direction”) relative to the display screen of the display panel 301, and to have refractive power in left and right directions (or a “horizontal direction”). The display screen of the display panel 301 includes a plurality of display pixels, which are aligned two-dimensionally in a regular manner. A back face of each of the cylindrical lenses 303 is arranged with two or more pixels. The stereoscopic vision is possible by causing light rays from the respective pixels to exit in different horizontal directions with the use of the refractive power of the lenses, so as to satisfy binocular parallax.
FIG. 19 illustrates an example of binocular stereoscopic displaying, where two adjacent pixel rows 301R and 301L in the display screen of the display panel 301 are allocated to each of the cylindrical lenses 303. The pixel row 301R as one row of pixels displays a right parallax image, whereas the pixel row 301L as the other row of pixels displays a left parallax image. The parallax images displayed by the pixel rows 301R and 301L are separated and distributed for discrete left and right optical paths 402 and 403 by the respective cylindrical lenses 303, respectively. Thus, when an observer 400 sees the stereoscopic device from a predetermined direction at a predetermined position, the left and the right parallax images properly reach left and right eyes 401L and 401R of the observer 400, and a stereoscopic image is thereby recognized by the observer 400.
Similarly, in an example of multi-eye stereoscopic displaying, a plurality of parallax images, which are taken from directions at positions corresponding to three or more viewpoints, are equally allocated to one lens-pitch of the cylindrical lenses 303 (more specifically, each lens-pitch of the cylindrical lens 303 in the horizontal direction), so as to be allocated for different optical paths and to be displayed stereoscopically. Thus, three or more parallax images are caused to exit for different but continuous angular ranges by the cylindrical lens array 302, and are imaged on the left and the right eyes 401L and 401R of the observer 400. In this example, the plurality of different parallax images are recognized by the observer 400 according to changes in position and direction of the viewpoint of the observer 400. The more realistic stereoscopic effect is obtainable when there are more changes in the parallax images corresponding to the changes in the viewpoint.
The cylindrical lens array 302 in the examples described above may be a lens array configured, for example, of a molded resin having a fixed shape and a fixed lens effect. However, a display device utilizing the cylindrical lens array 302 in this case is useable only for three-dimensional displaying due to the fixed lens effect. On the other hand, a switching lens-array element utilizing liquid crystal lenses may be used for the cylindrical lens array 302. The use of the switching lens-array element utilizing the liquid crystal lenses makes it possible to electrically switch over between presence and absence of the lens effect. Thus, modes of displaying are switchable between two displaying modes of a two-dimensional displaying mode and a three-dimensional displaying mode, by a combination with the two-dimensional displaying device. More specifically, in the two-dimensional displaying mode, the lens array is caused to have a state in which no lens effect is present (i.e., a state where no refractive power is present), so as to allow display-image light emitted from the two-dimensional displaying device to pass therethrough as it is. In the three-dimensional displaying mode, the lens array is caused to have a state in which the lens effect is generated to deflect the display-image light exiting from the two-dimensional displaying device into the plurality of viewing-angle directions, so as to thereby realize the stereoscopic vision.
FIG. 20A to FIG. 22 illustrate respectively an example of a configuration of the switching lens array element utilizing the liquid crystal lens. As illustrated in FIGS. 20A and 20B, the lens array element is provided with a first substrate 101 and a second substrate 102, and a liquid crystal layer 103 interposed between the first and the second substrates 101 and 102. Each of the first and the second substrates 101 and 102 is configured of a transparent material such as glass, for example. The first and the second substrates 101 and 102 are disposed to oppose each other with a gap distance “d” in between.
As illustrated in FIGS. 21 and 22, a first transparent electrode 111 is uniformly formed on the first substrate 101 substantially entirely on a side opposing the second substrate 102, whereas second transparent electrodes 112 are partially formed on the second substrate 102 on a side opposing the first substrate 101. Each of the first and the second transparent electrodes 111 and 112 is configured of a transparent conductive film such as an ITO (Indium-Tin oxide) film. As illustrated in FIG. 22, each of the second transparent electrodes 112 has an electrode-width of a width “L”, and extends in a vertical direction, for example. The second transparent electrodes 112 are arranged in parallel at an interval corresponding to a lens-pitch “p” (more specifically, the lens-pitch p at the time when the lens effect is generated). A spacing between the adjacent two second transparent electrodes 112 corresponds to an opening having a distance “A”. Note that, for the sake of describing the arrangement of the second transparent electrodes 112, FIG. 22 illustrates a state where a positional relationship between the first and the second substrates 101 and 102 are reversed, i.e., the first substrate 101 is on an upper side and the second substrate 102 is on a lower side, as compared with FIG. 21.
An alignment film (not illustrated) is formed between the first transparent electrode 111 and the liquid crystal layer 103. The unillustrated alignment film is also formed between the second transparent electrodes 112 and the liquid crystal layer 103. The liquid crystal layer 103 includes liquid crystal molecules 104 having a refractive index anisotropy, which are distributed uniformly in accordance with a direction of orientation defined by the alignment films.
In this lens array element, the liquid crystal molecules 104 are aligned uniformly in a predetermined direction defined by the alignment films, in a normal state in which an applied voltage is at zero volts as illustrated in FIG. 20A. Accordingly, a wavefront 201 of light rays, having passed through the lens array element, is in a form of plane wave, and thus the lens array element has a state in which no lens effect is present. On the other hand, since the second transparent electrodes 112 in the lens array element are separately disposed to have the opening including the distance A as illustrated in FIGS. 21 and 22, deviation occurs in an electric field distribution within the liquid crystal layer 103 when a predetermined driving voltage is applied in the state illustrated in FIG. 21. More specifically, such an electric field is generated in which an electric field intensity is stronger in accordance with the driving voltage in a portion corresponding to regions in which the second transparent electrodes 112 are formed, and is weaker as a distance from the portion increases toward the center of the opening of the distance A. Accordingly, the alignment of the liquid crystal molecules 104 changes in accordance with the distribution of the electric field intensity, as illustrated in FIG. 20B. Thus, the wavefront 202 of the light rays having passed through the lens array element are changed, and the lens effect is generated.
Japanese Patent Application Unexamined Publication No. 2008-9370 discloses a liquid crystal lens in which a portion corresponding to the second transparent electrodes 112 in the electrode configuration illustrated in FIGS. 21 and 22 has a two-layer structure. In this liquid crystal lens, an interval of arrangement of the transparent electrodes, formed on one side of a liquid crystal layer, is changed in a first layer and in a second layer. Therefore, control of an electric field distribution formed in the liquid crystal layer is optimized more easily.